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Author Topic: Jake Brake install  (Read 1331 times)
tuccitown
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« on: July 11, 2012, 11:42:13 AM »

Hi All,

I have been purchasing and collecting Jake Brake parts to install on my '79 GMC with an 8v71. The part that has eluded me is the fast idle buffer switch. To be honest I am not sure what the purpose of this switch is for. I am guessing that it will not allow the Jake Brake to be used if the rack is in a fuel delivery position. Is that correct? I have read that there are some that are not using the a buffer switch. Can someone explain to me the pros and cons of not using one? Also does anyone know where one could get a fast idle buffer switch? I've seen them new at about $700 is that my only option.

Thanks in advance as I am planning to replace the current 8v71 with the replacement I purchased and had planned to install the Jakes on the replacement engine before the swap.

Jack
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luvrbus
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« Reply #1 on: July 11, 2012, 11:59:19 AM »

Before spending the bucks for the combo fast idle buffer switch you can use a micro switch on the throttle and keep the fast idle you have now 

The King Cruise Control is another option best of 2 worlds you get cruise control and fast idle while using the cheaper buffer switch idle for a couple of hundred less than the fast idle buffer switch combo,There are dozens of ways to skin the cat lol I prefer the buffer switch myself the engine controls the Jakes with that setup


good luck
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thomasinnv
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« Reply #2 on: July 11, 2012, 04:14:47 PM »

I currently do not have a buffer switch installed. Works for me, but I think I am going to get a buffer switch and just eliminate the fast idle. I find I rarely if ever use it anymore. Or I may just go the micro switch on the throttle route. That would sure be a cheap alternative. The way it is now, I just make sure not to engage the jake unless the rpms are up and the foot is off the throttle.
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1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
lostagain
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« Reply #3 on: July 11, 2012, 06:44:53 PM »

A simple way to have the Jakes wired I have seen in a friend's bus is an off/on switch on the dash to turn the system on. Then a foot switch on the left on the floor, the kind that is closed only when you press it with your foot to engage the Jakes. The power goes directly from that to the Jakes. Does not involve the buffer switch. Works really well and is simple.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
luvrbus
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« Reply #4 on: July 11, 2012, 07:02:58 PM »

Jake and Detroit both recommend you to use the buffer switch system they do on all mechanical engines it takes the control away from the driver and lets the engine control it  

I will not install a set without the buffer switch or a micro switch on the throttle

I helped Derrick install his on his MCI but when it came to hooking it up direct he was on his own Lol I have saw Jakes wired about anyway possible my GM friends do some strange stuff and get away with most of the time some are not so lucky

good luck
« Last Edit: July 11, 2012, 07:20:20 PM by luvrbus » Logged

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bevans6
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« Reply #5 on: July 12, 2012, 06:40:43 AM »

I am thinking of what you could do with jakes if you felt like it...   Cool

The idea of the buffer switch is to make it so the jakes can't operate unless the engine is in no-fuel.  Obviously the jakes open the exhaust valves at basically TDC.  I wonder what would happen if you engaged the jakes when you were fueling the engine?  Maybe - the fuel would get out before ignition and create a big flame-thrower (or bomb in the muffler) or maybe the ignition event would happen just before the valves opened and a real flame thrower would happen with fully lit fuel being dumped in the exhaust manifolds...

Oh, the things we think about!  I am thinking big puller engine, straight pipes pointing straight up, way big injectors and correctly timed and set up jakes and flames up 20 - 30 feet by flipping a switch!   Grin

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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lostagain
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« Reply #6 on: July 12, 2012, 06:53:12 AM »

I remember driving my friend's Prevost mentioned above with the momentary Jakes switch at your left foot, and trying to give it fuel with the Jakes on. No flames, no big bang. Only no power with a bluh, bluh sound as the engine wanted to die. It had a manual transmission, so your left foot would be off the Jakes to shift gears. And any driver with a bit of common sense would stay off it unless needed. Somebody had done that install without asking Clifford first, LOL.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
Lee Bradley
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« Reply #7 on: July 12, 2012, 06:53:50 AM »

As I understand jakes, they stop the fuel igniting after the engine uses the energy required to compress the air. So with the fuel 'on' you would probably just have raw fuel in the exhaust and a great white cloud.
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luvrbus
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« Reply #8 on: July 12, 2012, 07:12:20 AM »

JC,I don't think you will get Don Fairchild to install a set without a buffer switch either lol
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thomasinnv
Derrick Thomas
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« Reply #9 on: July 12, 2012, 09:40:12 AM »

Lee, jake brakes really have nothing to do with fuel. When the jakes are applied the engine is in the no fuel position so no fuel is being supplied to the engine at all. what the jakes actually do is to release the compressed air at the top of the stroke, creating a zero pressure situation at the top of the stroke, so that as the piston goes back down it actually creates a vacuum. The compression of the upward stroke and vacuum of the downward stroke combined is what provides the "braking" energy. With no jakes, as the piston passes TDC the compressed air just pushes the piston back down. No braking effect. Gas engines don't need jakes because the carburetor (or throttle valve on fuel injected engines) cuts off the air intake when letting off the throttle, creating the same vacuum effect. The "phum phum phum" sound you hear when turning on the jakes is actually just the sound of compressed air being released from the combustion chamber.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
Lee Bradley
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« Reply #10 on: July 12, 2012, 10:24:39 AM »

What I meant by stopping the fuel from igniting, if there was fuel being injected, was that the compression is released so the heat required for ignition is missing. 
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tuccitown
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« Reply #11 on: July 12, 2012, 01:01:47 PM »

Thanks for all the replies, I think I will investigate the King cruise option. That comes with a buffer switch that can be used for the Jakes?

My plan is to have it setup so I won't have to do do anything but flip the high / low switch when I want the Jakes. Does anyone have the above configuration with the King cruise that wouldn't mind sharing there wiring diagrams?

Thanks again,

Jack
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lostagain
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« Reply #12 on: July 12, 2012, 03:01:59 PM »

Go to jakebrake.com. You will find installation manuals with wiring diagrams. Also try Jacobsvehiclesystems.com.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
Lin
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« Reply #13 on: July 12, 2012, 03:20:28 PM »

Jack, it is not that the King Cruise comes with a buffer switch, but rather that you can use the cruise control to set engine RPM's thus duplicating the effect of high idol.  You can add the cruise control now or later; it has nothing to do with your Jake installation.  We have just the regular buffer switch.  I have not missed high idol.  The couple of times I wanted the engine at higher RPM while I was checking something elsewhere, I just used a stick on the throttle.  The normal high idol setting would have been lower than I wanted anyway.
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RickB
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« Reply #14 on: July 12, 2012, 04:29:42 PM »

I hate to say it but I use Hi idle all the time... If I'm running the Bus AC I run it. If I'm filling up at the gas station I run it. Pretty much anytime my bus is idling it is hi idling
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